Functional principle of an underground pumped storage

An underground pumped storage power station utilizes the differences in altitude and the existing infrastructure of the mining industry. The RAG has visualized the functional principle in a short animation video.

Development of an implementation concept to use former coal mines for underground pumped storages

Developing renewable energy capacity and its increased integration in Germany’s energy supply is a current priority in energy policy. Fluctuations in electricity supply from renewable sources mean that storage technology is an important component of the necessary infrastructure. Up to now there have been no mature concepts put forward to resolve the problem of storing electricity. Because a combination of different storage technologies is likely, pumped storage plants can also be expected to make their contribution to the energy transition.

The project sets out to examine how far the extensive underground coal mining infrastructure in the Ruhr area is suitable for siting a pumped storage plant. A broad interdisciplinary team of researchers has been brought together to consider the many issues raised by the project.

The research team is made up of researchers from five chairs at the Universityof Duisburg-Essen, three at RuhrUniversity Bochum, the mining operator RAG AG, mining service provider DMT, and RISP, an associated institute of the University of Duisburg-Essen (>Partners).

The project is supported by the federal state of NRW and the EU as part of the Ziel 2 programme. The supervising authority is Arnsberg district government (Bezirksregierung Arnsberg) and the project management organization (ProjektträgerETN) at Forschungszentrum Jülich. Coordination is by the Institute of Hydraulic Engineering and Water Resources Management, University of Duisburg-Essen, under the leadership of Prof. Dr.-Ing. André Niemann.

Block picture Underground Pumped Storage (Click to enlarge)

Conventional pumped storage plants operate with an upper reservoir on a hill and a lower reservoir in the valley. The height difference between the two basins is exploited to store energy during periods of oversupply and release it again as required. Sites for such plants are limited by the topographical conditions and often controversial on account of the high land use associated with them.

The idea behind an underground pumped storage plant(UPS) is to move the lower reservoir below ground into existing coal mines and install the upper basin at the surface. This would create drop heights of up to 1200 metres with considerable potential for energy use. With the politically endorsed decision to end coal mining in 2018 already in place, the timing for examination of the potential of these plants is good. Up to that time, the mine shafts remain open before the constant rock pressure reseals them.

The aim of the project is essentially to examine the conditions for realization of an underground pumped storage plant in the RAG AG mines. The initial focus is on identifying the potential, estimating the feasibility of different types of UPS, and defining a final specific site. To do this, the geological and geographical conditions, technical and engineering complexity, and feasibility of construction and operation must be considered alongside the costs of storage, energy management and socio-ecological issues, and especially the level of acceptance and the work and operational safety of such plant. This will be accompanied by a legal and environmental assessment.

The project is to take place in two phases. In the currently funded first phase (18 months), an implementation concept in the same depth as a feasibility study is being prepared. Phase one is scheduled for completion in April 2014.